Hello .... A few weeks ago I bought the Janome 6600; but I did see and sew on the Janome 4120 QDC and really liked it. The 6600 has a few more features (and so, of course, was a few more $$$$). And I really like it. However, I did struggle a bit between the two, but I know, IF I had bought the 4120, I would not be able to upgrade to the 6600 later. We are retired and my husband loves these words: *fixed income* ... lol
The 4120 is a little smaller and cuter too!!! One thing I actually liked better on the 4120 was the LCD screen, it's blue and VERY EASY to read. The 6600 has a green screen; and I just think the blue is a little easier to see.
Good luck and happy quilting
jody